The present invention relates to an electric pole for a low-voltage power circuit breaker having improved features.
More particularly, the present invention relates to an electric pole for a low-voltage automatic power circuit breaker having improved reliability and ease of use.
It is known that a low-voltage automatic power circuit breaker is a circuit breaker used in industrial electrical systems characterized by operating voltages below 1000 volts and by electric currents whose nominal value can vary from fractions of an ampere to several thousand amperes, leading to relatively high power levels.
It is known that an automatic power circuit breaker comprises one or more electric poles, with each of which a phase electrical conductor or a neutral electrical conductor is associated. Depending on the number of electric poles used, an automatic power circuit breaker is termed single-pole, two-pole, three-pole, four-pole, et cetera.
Usually, an electric pole comprises two electrical contacts that can be mutually coupled/uncoupled. The electrical contacts are electrically connected to the phase or neutral conductor associated with the electric pole.
Generally, each electric pole of the circuit breaker comprises a current sensor associated with the phase or neutral conductor. The current sensor normally comprises a current sensing transformer, whose primary winding is constituted by the phase or neutral conductor and whose secondary winding is electrically connected, by virtue of electrical output terminals, to the protection unit of the circuit breaker, also known as overcurrent relay. Accordingly, at the output of the secondary winding the current sensing transformer generates sensing signals that are indicative of the value of the intensity of the current in the phase or neutral conductor. The sensing signals are sent in input to the protection unit, which provides in output control signals for an actuation device. In this manner, for each electrical phase it is possible to constantly sense the absorption conditions of the load, recognize any anomalies of operation and, if necessary in case of malfunction, overcurrent, short circuit, automatically open the circuit breaker.
It is known that the electrical connection of the current sensor to the protection unit can occur in various manners.
According to a first conventional approach, the current sensing transformer is connected to an electronic interface card, which in turn is electrically connected to the input section of the protection unit. In practice, the current sensing transformer is mounted on the electronic interface card and the electrical output terminals of the transformer, connected to the secondary winding thereof, are soldered to conductors formed on the electronic interface board. These conductors are connected electrically, by virtue of soldered junctions or appropriate connectors, to the electrical terminals of the input section of the protection unit.
An alternative conventional approach instead entails soldering appropriate electrical cables to the electrical output terminals of the transformer and connecting (by soldering or by means of appropriate connectors) said electrical cables directly to the electrical terminals of the input section of the protection unit.
Electric poles for low-voltage power circuit breakers of the known type have drawbacks.
These drawbacks arise from the fact that the electrical connection between the current sensor and the protection unit usually provides for a relatively large number of soldered joints and electrical junctions. During the operating life of the circuit breaker, these soldered joints and junctions can be subject to deterioration and separation, for example due to the considerable vibration to which the electric pole is usually subjected during disconnections. The operating efficiency of the circuit breaker therefore depends on the perfect state of preservation of the electrical connectors and cables. Therefore, it is quite often necessary to perform difficult and expensive maintenance interventions in order to ensure adequate reliability. Clearly this has negative repercussions on the overall manufacturing and operating costs of the low-voltage circuit breaker.